Pressure medium containers for hydraulic motor vehicle brake systems are known. Usually such pressure medium containers are mounted in the engine bay directly on the brake master cylinder or at least connected thereto hydraulically via lines. In many vehicle variants, the installation conditions present in the engine bay mean that pressure medium containers are used which are formed more linear than cuboid, because for example front windscreens with a shallow slope angle and at the same time a more compact construction of a brake actuating system mean that pressure medium containers must be arranged below the header tank.
In order to be able to receive the filling device for vacuum or pressure filling at the neck, such an arrangement means that the filler pipe is usually mounted at the front in the driving direction or on a front end of the pressure medium container. Because of such a decentralized arrangement of the filler pipe however, during driving operation or in transport, frequently during a braking process or when parking on a steep downhill gradient, the filler pipe is regularly flooded with the pressure medium.
The closing caps of generic containers usually have devices for pressure equalization with the surrounding atmosphere. To prevent the pressure medium from escaping through such a pressure medium equalization device during flooding of the filler pipe, complex systems are provided which are intended to guarantee a venting function and prevent an escape of the fluid, but at the same time these increase the complexity and production cost of the closing cap.